1. Field of the Invention
The present invention relates to a flood light for a camera and the like, for example, a flood light for both active and passive range finding devices.
2. Description of the Related Art
Various lights have been proposed and been put into practical use as flood lights for cameras.
For example, a flood light for a flood lighting type of range finding device disclosed in Japanese Unexamined Patent Publication No. 61-230110 is constructed so that light reflected by a spherical mirror can be cast from a flood lighting hole provided in the spherical mirror. A hole is provided in the spherical mirror for conveying the light from an emission means.
In addition, the auxiliary light casting device for range finding disclosed in Japanese Unexamined Utility Publication No. 1-75208 has emission means that is located inversely to the flood lighting direction. A beam emitted from the emission means is reflected by two concave mirrors whose ends are connected with each other.
Furthermore, in an auxiliary illumination device disclosed in Japanese Unexamined Patent Publication No. 8-54668, emission means is located at a focal position of a reflector having an oval cross-section, and at the same time, is located at the vicinity of a focal point of a flood lighting lens that has a positive refractive index and is provided before the emission means. Then, the direct light from the emission means is cast as a beam, and the light reflected by the reflector emerges as diffused light.
The conventional illumination devices referred to above, have defects that are referred to below.
That is, in the flood lighting type of range finding device disclosed in Japanese Unexamined Patent Publication No. 61-230110, a beam that is poured from an emitter or emission means (a light source) and enters into a spherical mirror, is directed to a subject after reflecting several times in the spherical mirror. Therefore, for the outgoing light beam energy loss becomes large. For this reason, it is necessary to increase brightness by using a plurality of emission means so as to obtain sufficient luminous energy. This, however, makes the shape of the flood light large.
In the auxiliary light casting device for range finding disclosed in Japanese Unexamined Utility Publication No. 1-75208, an emission side of faces reflecting surfaces of two concave mirrors connected in linear symmetry. Hence only beams reflected by these concave mirrors are used as the auxiliary light for range finding. Generally, a beam is not directed to a particular direction but is spread in various directions. But the above-mentioned concave mirrors cannot reflect all beams emitted from the emission means. In order to efficiently use beams from the emission means, enlargement of areas of the concave mirrors, or other measures, should be taken.
Furthermore, in an auxiliary illumination device as disclosed in Japanese Unexamined Patent Publication No. 8-54668, although the direct light from the emission means becomes a beam used for range finding, reflected light diffuses uselessly. The instant disclosure includes FIG. 14 which is a ray diagram drawn in accordance with a paraxial theory. In FIG. 14, among rays emitted from emission means 100, are both direct rays 113, and reflected rays 112 pouring into the convex lens 108 after reflecting from reflector 103. Direct rays 113 are illustrated with alternate long and short dash lines while reflected rays 112 are illustrated with solid lines.
As shown in FIG. 14, the reflected rays 112 pass through the convex lens 108 and diffuse in a range wider than a range where the range finding device performs range finding, and hence the rays do not exhibit an effect as auxiliary light. On the other hand, in regard to the direct rays 113, since there is a focus of the convex lens 108 nearby a light source, the rays emerge from the convex lens 108 in a beam. The direct rays exhibit the effect as the auxiliary light.
Thus, according to this construction, only a part of a bundle of rays emitted from the emission means are used as the auxiliary light. In addition, since the direct rays having the shape of the light source are cast as it is, the luminous intensity distribution of flood lighting is not uniform, as shown in the contour map of FIG. 15. Thus, a mountain in a center part is the direct ray and the foot of the mountain is the reflected rays that diffuse. These reflected rays diffuse in a comparatively wide range against the direct rays in the center part. Assuming that a range for range finding is a part illuminated by the direct rays, the reflected rays that diffuse illuminate places irrelevant to the range finding.
Therefore, according to the construction of the invention described in the above-mentioned Japanese Unexamined Patent Publication No. 8-54668, only a part of a bundle of rays emitted from the emission means are used as the auxiliary light. Furthermore, since rays in heterogeneous luminous intensity distribution are cast, correct range finding cannot be performed.
In this manner, none of the above-mentioned conventional art is an efficient user of the energy from the emission means. In order to increase luminance, it is necessary to take special measures such as enlarging the reflecting mirrors and refraction means, increasing the energy supplied to the light sources, and the like. For this reason, each of the above prior art technology a problem that results in increased space for a flood light utilized for a camera. In addition, each of the prior art arrangements described above produces a luminous intensity distribution that is not suitable for range finding.
Accordingly, an object of the present invention is to provide a small flood light, that has an high optical output by effectively using a bundle of rays emitted from emission means and desirable luminous intensity distribution.
A flood light of the present invention comprises emission means, reflection means that reflects rays from the emission means forwardly, and an optical element that is in front of the emission means and makes the rays from the emission means and the rays reflected by the reflection means pass through the optical element. Furthermore, the flood light is characterized in that a reflecting surface provided in the reflection means is constructed of a concave mirror, and the optical element is concave and has negative refracting power.